1. Field of the Invention
The present invention relates to a spread illuminating apparatus used as an illuminating means for signboards, various kinds of reflection-type displays and so on.
2. Conventional Art
Electric products nowadays have a function to display various information, and need to be equipped with a display portion to display the information. And, for portable electric products such as a mobile phone or a note-type personal computer wherein all components are expected to be miniaturized and light weight, a liquid crystal display (the ratio of thickness to display area is extremely small) has been widely used as the display portion because of its small occupation volume in the products and light weight. On the other hand, since the liquid crystal display does not emit light by itself, an illuminating apparatus besides the liquid crystal display apparatus needs to be provided when using in a dark area or at night. For realizing an illuminating apparatus capable of emitting light uniformly over the whole display portion, a below-explained illuminating apparatus has been invented.
A spread illuminating apparatus has a transparent substrate made of a transparent material and disposed on the front or rear surface of a liquid crystal display apparatus, and illuminates the entire liquid crystal display apparatus while illuminating the side surface of the transparent substrate to introduce light into the transparent substrate and then to uniformly supply the introduced light through the surface of the transparent substrate to the display portion of the liquid crystal display apparatus.
Now, a fluorescent tube (cold cathode ray fluorescent tube or hot cathode ray fluorescent tube) has been conventionally used as a light source to illuminate the side surface of the transparent substrate. However, a high voltage is needed for the fluorescent tube to emit light, accordingly a high voltage supplying means is required, resulting in conflict with the demand that portable product components be miniaturized and light weight. For solving the above-described problem, the present inventors have developed a spread illuminating apparatus applying a spot-like light source such as a light emitting diode, etc., and the present applicant has disclosed details in the Japanese Patent Application No. Hei 1-182076. The spread illuminating apparatus having a light emitting diode as a light source is briefly explained with reference to FIG. 7. The spread illuminating apparatus comprises a transparent substrate 2 overlapping on an upper surface of a liquid crystal element 1, and a bar-like light conductive member 3 disposed at the end of the transparent substrate 2, with a light emitting diode (LED) 4 disposed at the end of the light conductive member 3.
A number of grooves 2a (a light emitting element) shown in FIG. 8 are provided in parallel on the front surface (the upper surface in Fig.) of the transparent substrate 2. Further, a number of prism shaped portions 3a are provided in a longitudinal direction of the light conductive member 3. According to this structure, light emitted from the LED 4 first enters the light conductive member 3 and is refracted at the prism shaped portions 3a. And, the light progresses from the whole of the light conductive member 3 uniformly toward the transparent substrate 2. Further, the light having progressed into the transparent substrate 2 is refracted at the grooves 2a and emitted from the whole of the rear surface (the lower surface in Fig.) of the transparent substrate 2. As a consequence, a uniform brightness can be achieved over the entire liquid crystal element 1. An observer views the display of the liquid crystal element 1 through the transparent substrate 2, but the display of the liquid crystal element 1 is not visibly disturbed since the groove 2a is quite minute.
Now, the above-described spread illuminating apparatus has satisfied the demand for the uniform illumination on the liquid crystal display apparatus, but, such spread illuminating apparatus as shown in FIGS. 9 and 10 have been invented for a further increase in brightness. In the spread illuminating apparatus shown in FIGS. 9 and 10, the LED 4 illuminates the transparent substrate 2 directly, which eliminates any lose incurred in the light conductive member 3 (FIG. 7) and improves the brightness. Moreover, FIGS. 9 and 10 indicate only one LED 4 per transparent substrate 2, but it is possible to juxtapose a plural number of LEDand 4 at the end of the transparent substrate 2.
However, a problem newly occurs when applying this constitution. That is, light emitted from the LED 4 as a spot-like light source has directivity to some extent. Accordingly, as shown in FIGS. 9 and 10, the light which enters directly the transparent substrate 2 is adapted to emphasize an emitting distribution pattern (the range to be illuminated) A characterized by the LED 4 and illuminates especially brighter the portion right beneath the emitting distribution pattern A than other portions of the liquid crystal element 1, developing unevenness in brightness. Even if a plural number of LEDs 4 are juxtaposed at the end of the transparent substrate 2, such a problem has never been completely solved with the generation of dark and bright area in the brightness still remaining on the liquid crystal element 1.
The present invention has been made in the light of the above problem, and the object thereof resides in that a miniaturized and light weighted spread illuminating apparatus has a uniform illumination while realizing a high brightness.
In order to solve the above problem, according to a first aspect of the present invention, in a spread illuminating apparatus, in which a spot-like light source is disposed near the side of a transparent substrate made of a transparent material facing the transparent substrate, a control means for controlling the directivity of light entering the transparent substrate is provided between the transparent substrate and the spot-like light source.
According to the present invention, since the directivity of the light emitted from the spot-like light source is controlled by the control means before entering the transparent substrate, the emitting distribution pattern characterized by the spot-like light source can be modified by the time the light enters the transparent substrate.
According to a second aspect of the present invention, in the above spread illuminating apparatus, a light diffusion film as the above control means is disposed between the side surface of the transparent substrate and the spot-like light source. Further, according to a third aspect of the present invention, in the above spread illuminating apparatus, a prism sheet as the control means is disposed between the side surface of the transparent substrate and the spot-like light source. Moreover, according to a fourth aspect of the present invention, in the above spread illuminating apparatus, a concave lens-like sheet as the control means is disposed between the side surface of the transparent substrate and the spot-like light source. By applying these control means, the directivity of the light emitted from the spot-like light source is controlled, and the emitting distribution pattern characterized by the spot-like light source can be modified by the time the light enters the transparent substrate.
Further, according to a fifth aspect of the present invention, in the above spread illuminating apparatus, the control means is formed on the side surface of the transparent substrate. Since the control means can fulfill a given function when disposed between the transparent substrate and the spot-like light source, number of parts may be reduced while securing such function by forming the control means on the side surface of the transparent substrate as the present invention.
According to a six aspect of the present invention, in the above spread illuminating apparatus, the light diffusion characteristic of the control means is optimized in a manner that the diffusion characteristic is varied at each position based on the emitting distribution characteristic of the spot-like light source. By this constitution the emitting distribution pattern characterized by the spot-like light source can be modified more effectively.
Further, according to a seventh aspect of the present invention, in the above spread illuminating apparatus, the control means is formed with a given distance between the light emitting element provided on the transparent substrate and the spot-like light source. In the present invention, considering a feature that the emitting distribution pattern characterized by the spot-like light source spreads wider with an increase in the distance from the spot-like light source modifying the light directivity, the light emitting element of the transparent substrate is provided at a distance where the emitting distribution pattern is not recognised, whereby the uniform illumination by the spread illuminating apparatus can be realized.
Further, according to a eighth aspect of the present invention, in the above spread illuminating apparatus, the given distance is determined in consideration of how the directivity of the light emitted from the spot-like light source is modified. As mentioned above, the emitting distribution pattern characterized by the spot-like light source spreads wider with an increase in the distance from the spot-like light source modifying the light directivity. Therefore, in the present invention, the unevenness in the illumination due to a clear appearance of the emitting distribution pattern is prevented by measuring the distance from the spot-like light source.
Further, according to a ninth aspect of the present invention, in the above spread illuminating apparatus, the spot-like light source is disposed in a manner that the axis of the light emitted from the spot-like light source makes a given angle against a spreading surface of the transparent substrate, and a reflection means is provided to turn the axis of the emitted light in a direction parallel with the spreading surface of the transparent substrate. By this constitution, a distance between the spot-like light source and the transparent substrate is secured in a three dimensional positional relation.
Still further, according to a tenth aspect of the present invention, in the above spread illuminating apparatus, the control means is constituted by combining two or more control means for controlling the directivity of light described in the second to the ninth aspects. According to the present invention, the light directivity is controlled multiply before the light emitted from the spot-like light source enters the transparent substrate, whereby the emitting distribution pattern characterized by the spot-like light source is more effectively modified.